As most power sources operate most efficiently at certain rpm ranges. This is especially true for human power sources, for example as applied to human powered bicycles. For this reason, it is desirable that a transmission provide a number of different gear ratios to enable the power source to operate most often at its peak rpm range, where most of its torque is available. Transmissions that provide a large number of gear ratios, as is particularly desirable for human powered machines, are often very complex, delicate and often heavy. A number of potential designs for multi-speed transmissions have been developed. Some significant examples include the following.
U.S. Pat. No. 2,875,628, issued to Walter, is directed to a variable speed transmission having two identical conically shaped sets of gears each mounted on a shaft that are parallel to each other. Power is transmitted from one set to the other through a transmission gear, an idler gear that can freely rotate about a shaft which is guided in position by a rod. The gear can be shifted axially and stepwise by a handle. When shifting into adjacent gears are engaged a smooth trouble free shift is ensured by having every other gear in the set rigidly coupled to the shaft and these rigidly coupled gears frictionally engage the gears that are interposed between them. Frictional linings are interposed between all the gears and the friction force can be controlled by tightening the end clamps on the shaft.
U.S. Pat. No. 2,936,641, issued to Voelkl, is directed to a variable speed transmission having two sets of gears each forming a cone shaped assembly of gears of a different diameter, a power transmitting gear is coupled between the two sets of gears with its position and therefore the transmitted gear ratio being controlled by a hand wheel and lead screw. Two overrunning clutches are mounted between each of the gears and its supporting shaft. When the power transferred gear is positioned so as to engage two gears of each cluster smooth operation is provided by the overrunning clutches decoupling the power from the slower turning gear.
U.S. Pat. No. 1,528,574, issued to Schaum, and U.S. Pat. No. 6,802,229, issued to Lambert are directed to continuously variable transmissions having a cone shaped gear having helical tooth pattern that mesh with a spur gear.
U.S. Pat. No. 5,653,143, issued to Langevin, and U.S. Pat. No. 6,321,613, issued to Avidor are directed to variable ratio transmissions systems having a sliding spur gear that can be positioned to engage one of a plurality of conical gear wheels.
U.S. Pat. No. 4,630,495, issued to Smith is directed to a continuously variable ratio power transmission comprising two helically patterned cone shaped gears that provide a transmission that is continuous and in constant mesh and has a wide range of gear ratio.
It is an objective of the present invention to provide a durable, compact, lightweight transmission capable of providing a wide range of available gear ratios. It is a further objective to provide a transmission which is sealed from contact with dirt and other contaminates. It is yet a further objective to provide a transmission adaptable to use with either an inline or transverse final drive train. Finally, it is an objective to provide a transmission which can work without a clutching mechanism.
While some of the objectives of the present invention are disclosed in the prior art, none of the inventions found include all of the requirements identified.